FIG. 1A is a cross-sectional diagram of energy particles 12 (for example photons from a laser beam) passing through semiconductor substrate 10 showing normal absorption of photons. In FIG. 1A, incident photons carry the optical energy without causing any mass transport. The material layer absorbs the energetic particles, in which the absorption passes are classified into two categories: Linear and Nonlinear absorption. Normal absorption of photons in semiconductor material takes place when electrons which are excited from the valence band to the conduction band by inter energy band transition, so that the incident photons are absorbed into the solid when photon energy is larger than the energy band gap of the solid (semiconductor material). In metals and heavily doped conductive semiconductors, a large number of free carriers such as free electrons exist in the conduction band. These free carriers may also absorb the incident photons (through free-carrier absorption) and are categorized as linear absorption since the number of absorbed photons is equal to the number of free carriers.hv>Eg(bandgap energy);Linear absorption
If photon energy is lower than the energy band gap (Eg), for example in a solid, the photons are not absorbed and are transparent. Product of h and v is photon energy where h is Planck constant and v is frequency.hv<Eg(bandgap energy);Transparent
On the contrary, FIG. 1B is a cross-sectional diagram of incident optical energy particles 16 (for example a laser) passing through lens 19 and semiconductor substrate 14 showing abnormal absorption of photons at selected material site/spot 18 (also referred to herein as a focal point within the material layer). Abnormal absorption may occur even in a transparent material/medium by linear absorption, for example with pulsed nanosecond laser focusing and nonlinear absorption with so-called multi-photon absorption in picoseconds pulse in which photons may be absorbed in multiple numbers per electron in (intra) the energy band gap or avalanche mode in conduction band.n×hv>Eg;Nonlinear absorption                (n=2, 3, 4, . . . )        
Where, n represents an integer number. This phenomenon occurs when the energy is deposited in a small concentrated space, such as the selected site/spot 18 in FIG. 1B, and in short time (high power focused at a small area or volume in very short time), that is using high peak power and shorter pulses of laser irradiation. Using such conditions and when a short pulsed laser beam is irradiated on the solid, melting and/or ablation of the material often occurs in the linear absorption regime (this effect may often be observed without tight focusing into a very small material volume).
Consider the case for choosing photon wavelength for solid material to be transparent to the beam and tightly focusing the beam inside the solid. The laser beam penetrates internally up (or down) to a depth from the solid surface and is then absorbed at a small site with dense energy concentration, resulting in some inhomogeneity formed in uniform matrix of the solid material. This occurs because the unfocused laser power is not absorbed due to the material transparency, while the tightly focused beam spot within the solid material triggers enhanced light absorption due to increased light absorption coefficient during heating as shown by the graph in FIG. 2.
The inhomogeneity (and micro-cracks) induced by focused laser beam using short laser pulses inside the solid material may produce the following effects:                1. Index of Refraction shift in the solid material;        2. Phase transition from Solid to Liquid or sublimation and solidification;        3. Crystallographic phase change to amorphous phase (and other possible phase changes);        4. Crystallographic defects formed as dislocations, corresponding array, twins, and grain boundaries from small angles to large ones;        5. Cracks (micro-cracks) by breaking atomic bonds resulting in space or micro-voids between bonds;        6. Cavity, void, or pores on micrometer scale breaking a mass of bonds and diffusing out in solid phase due to abnormal local heating.        
The index change has been observed in glass and has application in waveguides and sculpturing within glass.
In mono-crystalline silicon and other semiconductor materials, longer wavelength photons using, for example a micrometer-scale focused beam, may penetrate transparently through the material to a specified site since the material's energy band gap is greater than the photon energy (hv<Eg) and the laser is focused by optical lenses tightly at the sites under the surface while using short laser pulses. However, under such conditions the material crystallographic phase often changes from crystalline phase to amorphous state, and/or changes from single-crystalline structure to polycrystalline phase, in conjunction with crystallographic defects, dislocations, twins, grains and corresponding array and boundaries at the specified site (often relatively small site) where the laser beam is focused to cause linear and/or nonlinear absorption. Such inhomogeneity in the uniform matrix of mono-crystalline wafers often introduces a large amount of stress localized at the selected sites, resulting in breakage of Si—Si bonds in the proximate vicinity of the selected site which leads to micro-cracks. Formation of cavities, voids, and pores may also take place under extreme conditions of abnormal light absorption due to increased light absorption coefficient during heating.